(Adapted from the applicant's abstract) The purpose of the hematopoietic stem cell/fluorescence activated cell sorter (HSC/FACS) Core is two- fold: 1) Provide phenotypically identified hematopoietic progenitor (CD34+) and stem cells (CD34+CD38-) for both the basic and clinical projects; 2) Analyze cell populations by flow cytometry to determine expression of differentiation antigens, markers of retroviral transduction, or cell cycle analysis.